I had a working Ethernet program but needed to add an SPI DAC. I started adding SPI code and then realized my Ethernet stopped working (along with an LCD I have connected for debugging).

My sketch also uses the hardware quadrature encoder setup. When the SPI messed up the Ethernet and LCD I did notice the interrupt routine for the encoder was still working fine so that ruled out a processor lockup or software crash (I believe).

Thinking it was my inexperience with SPI, I copied my sketch and deleted all Ethernet related code and worked on the SPI until it was fully functional. I then started added back my Ethernet stuff and found that when I hit the Ethernet.begin line things went bad again.

I'm using pin52 for my SPI DAC select. My SPI is set to mode1. My LCD is on pins (33,31,29,27,25,23). I'm using arduino 1.5.4r2.

It almost acts like when both SPI & Ethernet are enabled the board becomes interrupt bound (explaining why printing to the LCD stops) except the logic analyzer I have connected to the SPI shows it has stopped too.